1. Field of the Disclosure
This disclosure relates generally to methods and apparatus for dispensing a viscous material on a substrate, such as a printed circuit board, and more particularly to a method and an apparatus for calibrating or otherwise verifying an amount of material dispensed on a substrate with enhanced efficiency.
2. Discussion of Related Art
There are several types of prior art dispensing systems used for dispensing precise amounts of liquid or paste for a variety of applications. One such application is the assembly of integrated circuit chips and other electronic components onto circuit board substrates. In this application, automated dispensing systems are used for dispensing very small amounts, or dots, of viscous material onto a circuit board. The viscous material may include solder paste or liquid epoxy, or some other related material.
There are known methods for calibrating a dispensing system to accurately control the rate and amount of viscous material that is dispensed from a dispensing unit of the dispensing system. One issue is that solder paste, for example, is difficult to dispense for calibrating the accuracy of the dispensing system since the amount of solder paste deposited cannot be accurately controlled. A quantity of material may be dispensed and weighed to determine if the unit is dispensing the desired amount of material for a given configuration of the system. One approach is to adjust the speed of the gantry carrying the dispensing head based on the weighed sample or samples to vary the amount deposited by the dispensing system. Another approach is to adjust the shot size dispensed by the dispensing head. One such system is shown and described in U.S. patent application Ser. No. 13/072,355, filed on Mar. 25, 2011, and entitled METHOD AND APPARATUS FOR CALIBRATING DISPENSED DEPOSITS, which is owned by the assignee of the present disclosure and incorporated herein by reference in its entirety for all purposes.
Another approach is described in U.S. patent application Ser. No. 13/598,719, filed on Aug. 30, 2012, and entitled METHOD AND APPARATUS FOR CALIBRATING DISPENSED DEPOSITS, which is owned by the assignee of the present disclosure and incorporated herein by reference in its entirety for all purposes. With this approach, a line of material, such as solder paste, is dispensed which has a material dispensing unit that is configured to dispense material on a substrate. Next, one or more images of the line are taken by an imaging system, and an average line width of the line is calculated. After determining the average line width, it is compared to a desired line width, which may be predetermined. The dispensing system includes a controller that is configured to perform the method and to provide closed loop determination on whether a proper amount of material is dispensed by the dispensing system.